High temperature low thermal expansion ceramic

ABSTRACT

This invention relates to the high temperature stabilization of aluminum titanate and aluminum titanate-mullite compositions by the addition of iron oxide. It has been found that iron oxide concentrations greater than 5 weight percent and as high as approximately 25 weight percent have a stabilization effect at high temperatures on aluminum titanates. The resultant ceramic body is further enhanced by the addition of from 0.1 to 5 weight percent rare earth oxide.

BACKGROUND OF THE INVENTION

This invention relates to the high temperature stabilization of aluminumtitanate and aluminum titanate-mullite compositions by the addition ofiron oxide. It has been discovered that iron oxide concentrationsgreater than 5% and as high as approximately 25% by weight have astabilization effect at high temperatures on aluminum titanate. Thiseffect is uncommon to prior stabilization attempts.

Aluminum titanates may be effectively used as filters for fluids, inparticular, as diesel particulate filters and as substrates forcatalytic converters, an example of which is known commonly in the artas a honeycomb substrate. Additionally, aluminum titanates are desirablein applications where the thermal shock resistance and the ultimate usetemperature are high. Cellular substrates used under conditions of highthermal gradients are examples of this application. Typically,structures such as the above are subjected to harsh environments whichrequire high thermal shock resistance, low thermal expansion, and highmechanical properties. Skilled workers in the art appreciate thatmaintaining these properties for extended periods of time in theirintended environments eliminates many potentially useful refractorymaterials. The reordering of crystalline phases, which commonly occursin ceramic materials subjected to these environments, impairs thedesired physical and chemical properties. The result is a degradedstructure which is no longer appropriate for its intended use.

It is known in the art that the inclusion of rare earth oxides and ironoxides to compositions consisting essentially of aluminum titanate,provides the body with sintering aids and further increasesstabilization to high temperature degradation. It has not beenconclusively determined how the stabilization is effected, although itis known that Fe₂ TiO₅ is in solid solution with Al₂ TiO₅. The solidsolution is effected during firing, and is facilitated at hightemperatures, above about 1400° C. The role the rare earth oxide playsis to affect the grain growth behavior, thus adding mechanical strength.

It has been found with the present invention that the addition ofsurprisingly large amounts of Fe₂ O₃ may be incorporated in the Al₂ TiO₅matrix. This combination may then be subsequently extruded and sinteredto form a honeycomb structure. The resultant structure produces athermally durable product with improved physical properties, unknown tothe prior art.

In U.S. Pat. No. 4,483,944 (the U.S. Pat. No. 4,483,944), an aluminumtitanate-mullite ceramic composition is disclosed which includes 0.5 to5% iron oxide and 0.5 to 5% rare earth oxides. In the U.S. Pat. No.4,483,944 it was disclosed that 0.5 to 5% iron oxide and 0.5 to 5% rareearth metal oxides will most desirably be present to serve as asintering aid and to inhibit the decomposition of Al₂ O₃. TiO₂ crystalswhen exposed to high temperatures.

U.S. Pat. No. 4,327,188 (the U.S. Pat. No. 4,327,188) discloses the useof aluminum titanate with the rare earth and iron oxide additives. TheU.S. Pat. No. 4,327,188 discloses that there is a disadvantage to addingmore than 2 weight percent of the specific additive due to an increasein the thermal expansion and a decrease in the melting point.

That there is a trade-off between the thermal properties and long lifeof aluminum titanate bodies has been known to the art. A remainingdifficulty in the art is to insure stabilization of the additive-ladenaluminum titanate body. A goal has been to find a body that canwithstand temperatures in excess of 1400° C. and maintain thecrystalline integrity at lower temperatures. The body should be able towithstand, without significant decomposition, extended use attemperatures between approximately 1000° C. and 1300° C. This propertyis important since it is well known to those skilled in the art that Al₂O₃. TiO₂ will decompose into corundum and rutile when exposed totemperatures within the above cited temperature range. To guard againstthis decomposition, it is necessary to thermally stabilize the aluminumtitanate phase.

Therefore, the primary objective of the present invention was to developan aluminum titanate-containing body which exhibits high mechanicalstrength, a low linear coefficient of thermal expansion, is capable ofextended use at temperatures in the vicinity of 1400° C., whilemaintaining crystalline integrity after very prolonged exposure totemperatures within the range of 1000-1300° C. Additionally, the body iscapable of repeated cyclings in the temperature range between roomtemperature and well over 1000° C. without significant change indimensional integrity.

SUMMARY OF THE INVENTION

We have found that the above objective and others that will beillustrated below can be attained in ceramic bodies consistingessentially of five basic components; viz., Al₂ O₃, TiO₂, SiO₂, rareearth oxide (expressed as RE₂ O₃), and iron oxide (expressed as Fe₂ O₃).Fundamentally, the bodies consist essentially of two crystal phases;viz., aluminum titanate (Al₂ TiO₅) and mullite (3Al₂ O₃.2SiO₂). Becauseof the ready reaction of Fe₂ O₃ with TiO₂, however, at least a portionof the aluminum titanate phase present in the inventive products mayactually consist of a solid solution containing Fe₂ TiO₅. Such solidsolution is readily apparent from a study of x-ray diffraction patternsproduced by the crystals. Hence, the typical overall pattern of aluminumtitanate is present, but the d-spacings and intensities are slightlyaltered. Accordingly, the expression aluminum titanate solid solutionwill be used in the description to generally identify the aluminumtitanate containing crystals.

The consolidation of alumina, titania, and iron oxide provide a bodywith excellent thermal decomposition properties. However, theenvironment of eventual use demands a ceramic body with good thermalshock resistant properties and high mechanical strength. Therefore, tomake the ceramic body useful for its intended environment, strengtheningcomponents must be added. Additives must be chosen so that strength isadded to the body without interfering with the desirable thermalproperties. The present invention contemplates the use of rare earthoxides and mullite to solve this problem.

As expressed in terms of weight percent on the oxide basis, theinventive compositions consist essentially of about 1.5-20% SiO₂, 0.1-5%RE₂ O₃, 225-25% Fe₂ O₃, 35-75% Al₂ O₃, and 10-40% TiO₂, wherein the rareearth metal is selected from the group consisting of La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Er, Yb, Y, Sc, and mixtures thereof. The preferredcompositions consist essentially, expressed in terms of weight percenton the oxide basis, of about 5-20% SiO₂, 0.1-5% RE₂ O₃, 225-25% Fe₂ O₃,40-65% Al₂ O₃, and 10-35% TiO₂, and the most preferred compositionsconsist essentially of 10-20% SiO₂, 0.1-5% RE₂ O₃, 8-25% Fe₂ O₃, 45-60%Al₂ O₃, and 15-30% TiO₂. Amounts of Fe₂ O₃ in excess of 5% (e.g. atleast 8%) are demanded to impart the desired resistance to thermaldecomposition of the aluminum titanate crystals; i.e., to insure thestabilization of the aluminum titanate crystals. Above 25% Fe₂ O₃,however, thermal deformation and actual melting of the products havebeen observed at temperatures in the vicinity of 1400° C.

Iron-aluminum oxide or titanate solid solutions within the invention canconsist essentially of, by weight percent, 30 to 75 percent alumina, 20to 65 percent titania, and optionally, greater than 5% to 25% iron oxideexhibit excellent thermal stability. This thermal stability wasindicated by x-ray diffraction patterns. The patterns revealed that thesolid solution decomposition products of Al₂ O₃, Fe₂ O₃, and TiO₂ wereless than 20 percent of the total stoichiometric decomposition. Thebodies had been heat treated within the temperature range ofapproximately 1000° C. to 1300° C. A preferred solid solution consistsessentially of, 35 to 50 percent alumina, 40 to 42 percent titania, and8 to 25 percent iron oxide. The most preferred solid solution consistsessentially of 35 to 50 percent alumina, 40 to 42 percent titania, and15 to 25 percent iron oxide.

Any of the practices conventionally employed in the ceramic art forforming finely-divided powders into shapes of a desired configurationare applicable with the inventive compositions. Such methods include drypressing, hot pressing, slip casting, isostatic pressing, hot isostaticpressing, and extrusion. For example, where the inventive materials areto be used as filters for fluids or as substrates for catalyticconverters, they can be readily extruded into honeycomb structures.

In general, sintering temperatures over the interval of about1400°-1650° C. will be utilized. Nevertheless, it will be recognizedthat through the use of expedients known to the ceramic art, such as theuse of substantial amounts of sintering aids, the use of calcined orprereacted clinker as a portion of the batch, and the careful choice ofbatch materials, the firing temperatures required can be reduced. Itwill be appreciated, however, that the applications to which the firedbodies are to be exposed for extended periods will involve temperaturesbelow that at which the bodies were sintered. Hence, the shrinkageundergone by a body during sintering is a function of the firingtemperature employed. Accordingly, where a body is subsequently exposedto a temperature above that at which it was sintered, further shrinkagewill occur which may render the body unusable for a particularapplication. Typically, the shrinkage experienced by the inventivebodies sintered over the temperature interval of 1400°-1650° C. willrange about 2-15%, the level of shrinkage increasing as the temperatureis raised.

Where the inventive products are to be used in fluid filter applicationsor as substrates for catalytic converters, porosity of the body and thesize of the pores are important. As can be appreciated, the totalporosity and the size of the pores are directly influenced by thetemperature at which the body is sintered; hence, the higher thetemperature, the lower total porosity and the smaller the average poresize. To illustrate, open poosity in the inventive products will averageabout 30-50% when a sintering temperature of 1400° C. is employed;whereas at a firing temperature of 1650° C., the average is decreased toabout 5-15%. The average pore size varies between about 1-15 microns,the size being generally smaller at the higher sintering temperatures.

Microscopic examination of the sintered inventive products has revealedthe presence of extensive very fine intracrystalline and grain boundarycracking similar to that described in the U.S. Pat. No. 4,483,944patent. As was explained there, these forms of microcracking permit thebodies to yield under thermal stress, thereby conferring upon the bodiesexcellent resistance to thermal shock. It appears that more of suchmicrocracking occurs as the sintering temperature is raised.

X-ray diffraction analyses have indicated the microstructure of theinventive products to consist essentially of aluminum titanate solidsolution and mullite with a very minor amount of rare earth metal oxide.Microscopic examinations have shown that the rare earth metal oxides aregenerally located along the grain boundaries of the mullite crystals andaluminum titanate solid solution crystals. It has been postulated thatthe rare earth metal oxides act as grain growth inhibitors with respectto the solid solution crystals. Such action is especially beneficialwhen the inventive bodies are fired at high temperatures and/or aresubsequently exposed to high temperatures. In general, the aluminumtitanate solid solution crystals tend to grow in size as the temperatureis increased. Through x-ray diffraction analyses and electronmicrographs it has been estimated that, by volume, the content ofaluminum titanate solid solution crystals ranges about 25-90% and thecontent of mullite crystals varies about 5-70% with the rare earth metaloxide comprising up to the remainder. A preferred composition of thissolid solution is 50 to 75 percent iron-aluminum titanate solidsolution, 20 to 50 percent mullite, and 0.1 to 5 percent rare earthoxide.

We have found that this invention provides an aluminum titanate basedbody wherein the linear coefficient of thermal expansion (25°-800° C.)ranges between -25×10⁻⁷ per °C. and 25×10⁻⁷ per °C. and measurements ofmodulus of rupture (MOR) by the four point bend method, range from 1000psi to 9000 psi.

And finally, our invention provides an aluminum titanate based ceramicbody with a coefficient of thermal cycling growth approachingapproximately 200×10⁻⁴ % per cycle, with the most preferred embodimentexhibiting a coefficient of thermal cycling growth approaching 25×10⁻⁴.

DETAILED DESCRIPTION

FIGS. 1 and 2 show x-ray diffraction results of isothermal heattreatment data which include prior art compositions and the titanatesolid solution for the present inventive compositions, treated for 512and 1024 hours, respectively.

The prior art, Examples 1, 2, and 3, exhibit the heretofore knowndecomposition results characteristic of aluminum titanate bodies exposedto the 1000° C. to 1300° C. temperature range. It is noteworthy thateach composition tested exhibited a maximum decomposition atapproximately 1100° C. when tested for 512 hours. The decompositioneffect broadens as the testing time is lengthened to 1024 hours,extending the maximum decomposition of the aluminum titanate body to ahigher and lower temperature range. The percent of decomposition isdetermined by x-ray diffraction. When a sample thermally decomposes, thex-ray diffraction pattern exhibits prominent Al₂ O₃ and TiO₂ peaks. Thearea under the peaks is proportional to the amount of aluminum titanatethat has decomposed into its constituent molecular forms, titania andalumina.

The titanate solid solution compositions of the present invention, thoseembodied by Examples 4, 5, 6, and 7, as in FIGS. 1 and 2, exhibitremarkable durability to thermal decomposition, when compared to thesame temperatures as those experienced by Examples 1, 2, and 3. Therewas no greater than 20 percent decomposition exhibited by the titanatesolid solution of the inventive compositions.

Table 1 shows the compositions of the iron-aluminum titanate solidsolution phase of these Examples. There is a marked difference inthermal durability between Examples 3 and 4 where the primary differencein the compositions is the increase in iron oxide concentration.

                  TABLE 1                                                         ______________________________________                                        Concentrations in Weight Percent                                              Example   Al.sub.2 O.sub.3                                                                            TiO.sub.2                                                                            Fe.sub.2 O.sub.3                               ______________________________________                                        1         56.10         43.90  0.00                                           2         55.33         43.79  0.88                                           3         52.43         43.25  4.32                                           4         48.91         42.58  8.51                                           5         45.49         41.94  12.57                                          6         42.17         41.31  16.52                                          7         35.83         40.05  24.05                                          ______________________________________                                    

The compositions in Table 1 were batched, fired, and tested for thermaldurability at 512 and 1024 hours. Thermal shock resistance isproportional to the thermal expansion coefficient. Therefore, it can beinferred from FIGS. 1 and 2, that thermal shock resistance for heattreated samples within the temperature region of approximately 1000° C.to 1300° C. is greatly enhanced for the compositions in Examples 4through 7. The enhancement is evidenced by the lack of significantincrease in thermal expansion. It has been found that too much ironoxide, greater than 25 weight percent, causes the body to slump onfiring, and in some cases the body melted.

Once the thermal properties of the solid solution of iron and aluminumtitanate bodies were determined, the bodies were mixed with mullite andrare earth oxides to determine if a composite body of this compositionwould exhibit desirable mechanical properties. Samples batched, as inExamples 4 through 7 in Table 1, were mixed with rare earth oxides andmullite. Advantageously, the rare earth oxides, such as the nitrate saltmixture of lanthanum and neodymium in concentrations ranging from 0.1 to5 weight percent, were mixed with the titanates before mixing withmullite and fired in the body as a sintering aid and grain growthinhibitor. The addition of the rare earths and mullite did notnegatively affect the desired thermal stability or expansion propertiesof the high iron titanate body.

The resultant ceramic body exhibits high thermal shock resistance, lowthermal expansion, and high mechanical strength. The linear coefficienitof thermal expansion (25°-800° C.) of the composition corresponding toExample 9 is approximately 21.1×10⁻⁷ and that of the correspondingExample 12 is approximately -8×10⁻⁷ per ° C. This thermal expansionrange indicates that the material has a low thermal expansion over thetemperature range of interest. The four point bend MOR's for the samemullite, rare earth additions to Examples 4 and 7 ranged from 1000 psito 9000 psi, respectively.

Shown in Table 2 are the results of the four point bend Modulus ofRupture (MOR) tests performed on 5/16 inch round cross sectional rods ofthe high iron-aluminum titanate solid solution, mullite, and rare earthceramic bodies. The compositions, in weight percent, track very closelyto those of Examples 3-7 in Table 1.

                  TABLE 2                                                         ______________________________________                                                                                   CTE                                Ex-                                        × 10.sup.-7 /°C.      am-                                        (25°-                       ple  SiO.sub.2                                                                            Al.sub.2 O.sub.3                                                                      TiO.sub.2                                                                          Fe.sub.2 O.sub.3                                                                    RE.sub.2 O.sub.3                                                                    MOR   800° C.)                    ______________________________________                                        8    8.46   54.78   28.94                                                                              5.78  2.04  3010  -.7                                9    8.46   45.89   27.27                                                                              16.34 2.04  4850  21.1                               10   14.10  53.30   19.48                                                                              11.67 1.45  5820  --                                 11   14.10  56.37   20.05                                                                              8.02  1.46  3350  8.1                                12   8.46   50.20   28.07                                                                              11.23 2.04  4250  -8.0                               ______________________________________                                    

The levels of the representative mullite phase in the above Examples8-12 were, respectively, 30, 30, 50, 50, and 30 percent. These sameExamples exhibited little or no decomposition when analyzed by x-raydiffraction, after being heat treated, similar to those Examples inFIGS. 1 and 2. All Examples in Table 2 exhibited significantimprovements over the prior art samples exhibited in FIGS. 1 and 2.Although the coefficient of thermal expansion increased in Examples 8,9, and 11 over the Examples of FIGS. 1 and 2, the thermal expansionexhibited is well within the limits desirable for good thermal expansionproperties.

Table 3 shows the results of MOR tests performed on samples lackingmullite and rare earth oxides. The compositions are given in weightpercent and the MOR values in psi.

                  TABLE 3                                                         ______________________________________                                        Example   Al.sub.2 O.sub.3                                                                      TiO.sub.2  Fe.sub.2 O.sub.3                                                                    MOR                                        ______________________________________                                        13        52.43   43.25      4.32  164                                        14        48.91   42.58      8.51  142                                        15        42.17   41.31      16.52 183                                        16        35.83   40.12      24.05 269                                        ______________________________________                                    

The addition of the mullite and rare earth oxides produces more than anorder of magnitude difference in the mechanical strength as measured bythe four point bend test. Comparisons between the two tables are inexactsince the normalized values of the compositions change as theconstituent oxides change. The range, however, of the iron titanatephase is sufficiently broad to indicate that within this range, thevalues of mechanical strength vary by not more than 70 to 80 percent.This indicates that changes in the composition, therein, do notcritically change the mechanical strength of the body. Higher processingtemperatures, such as those greater than 1500° C., will lead to CTEsbounded by -20×10⁻⁷ /° C.

When the MOR measurements in Table 3 are compared to those exhibited bythe mullite, rare earth, iron aluminum titanate Examples in Table 2, itis easily concluded that for the same approximate solid solution phase,titanate compositional range, Table 2 Examples show the desired andcritical increase in measured strength (more than 2000% over that inTable 3). Therefore, the addition of mullite and rare earth oxides tothe high iron titanate body significantly increases mechanical strength,as inferred from the MOR measurements. This increase in strength, aswill be shown below, does not significantly compromise the thermalproperties of the high iron titanate body.

The body of the inventive composition consists essentially of Al₂ TiO₅,Fe₂ TiO₅, rare earths, and mullite. Those skilled in the art willappreciate that there are several methods available to intermix thesecomponents to effect the advantages afforded by this composition. Table4 shows the as-analyzed composition of a preferred embodiment of theinvention.

                  TABLE 4                                                         ______________________________________                                        Component     Weight Percent                                                  ______________________________________                                        Al.sub.2 O.sub.3                                                                            56.13                                                           SiO.sub.2     13.90                                                           TiO.sub.2     20.35                                                           Fe.sub.2 O.sub.3                                                                            8.14                                                            Re.sub.2 O.sub.3                                                                            1.50                                                            ______________________________________                                    

A preferred method to prepare the composition in Table 4 is essentiallya two-step process. The first step was to mix 37 weight percent of Al₂O₃ with the Fe₂ O₃ (a pigment grade hematite), and the TiO₂. Theparticle size distribution of these components was preferably -100 mesh(less than 149μ diameter). The powdered components were placed in aLittleford mixer and blended for a period of 5 minutes. This materialwas transferred to a Simpson mixmuller and combined with water and anorganic binder, such as methylcellulose, to form agglomerates of themixture. The water addition contained a solution of 3 weight percentrare earth nitrate. The rare earth nitrate was a solution of La/Nd in a75/25 by weight proportion, respectively. The rare earth component maybe optionally added to either step in the process without significantloss of properties in the resultant body. The agglomerated material wasair-dried for 24 hours, transferred to alumina vessels, placed in aperiodic kiln, and fired at 1400° C. for 6 hours. The resultantcomposition consisted essentially of a single phase solid solution ofFe₂ TiO₅ and Al₂ TiO₅. The rare earth oxides reside principally at thegrain boundaries to control grain growth behavior.

The calcined agglomerates were ground to -100 mesh with a preferredmedian particle size of approximately 40μ. Initially, the agglomerateswere ground in a jaw crusher and subsequently ground by ball millingwith α-alumina grinding media. After ball milling, the powder was sievedand the particle size measured.

In the second step, the calcined powder was transferred to a Littlefordmixer and mixed with the remaining components to form the preferredcomposition in Table 4. The additional components of 14.10 weightpercent SiO₂ and 12.14 weight percent Al₂ O₃ were added in the form ofkaolinite clay. The remaining 7.00 weight percent alumina was added inthe form of α-alumina in this step to provide the total composition of56.13 weight percent alumina. The total mix was blended in a Littlefordmixer for 5 minutes.

The powdered mixture was transferred to a Simpson mix-muller,plasticized, and extruded according to standard extrusion practicesknown in the art. Water was removed from the cellular ware usingdielectric dryers, and the honeycomb pieces were subsequently firedbetween approximately 1400° C. and 1650° C.

To compare the properties of the inventive composition with a prior artcomposition, samples were prepared according to the composition in Table5 and the above preferred method.

                  TABLE 5                                                         ______________________________________                                        Component     Weight Percent                                                  ______________________________________                                        Al.sub.2 O.sub.3                                                                            59.29                                                           SiO.sub.2     13.68                                                           TiO.sub.2     21.28                                                           Fe.sub.2 O.sub.3                                                                            4.25                                                            Re.sub.2 O.sub.3                                                                            1.50                                                            ______________________________________                                    

Examples from Table 4, the inventive composition, and Table 5, a lowiron prior art composition, were subjected to isothermal heat treatmentat 1000° C., 1100° C., and 1200° C., for 1024, 537, and 1024 hours,respectively. The treated Examples were analyzed by x-ray diffraction todetermine the extent of decomposition from the solid solution to Al₂ O₃and TiO₂. The composition of Table 5 exhibited pronounced peaks at theTiO₂ and Al₂ O₃ peak sites hence, evidencing the substantialdecomposition observed in Examples 1, 2, and 3 in FIGS. 1 and 2. TheExample from Table 4 exhibited smaller peak heights, thereby indicatingsignificantly less decomposition. The latter peak heights were quiteanalogous to the percent decomposition exhibited by Example 4 in FIGS. 1and 2.

These tests indicate that the addition of mullite and rare earths,individually or collectively, to the Fe₂ TiO₅ and Al₂ TiO₅ single phasesolid solution does not interfere with the advantageous propertiesexhibited by the solid solution examples of the invention in FIGS. 1 and2. The resultant mullite and rare earth enriched body is fortified withthe thermal shock resistant property attributed to the iron richaluminum titanate phase, and continues to benefit from the mechanicalstrength properties added by the mullite and rare earths. The body ofthe inventive composition is capable of withstanding the criticaltemperature range without the loss of thermal expansion and/ormechanical strength properties.

We claim:
 1. A sintered ceramic article containing iron-aluminumtitanate solid solution and mullite as the predominant crystal phaseswith a minor amount of a rare earth metal oxide crystal phases, saidarticle exhibiting grain boundary and intracrystalline microcracking andconsisting essentially, expressed in terms of weight percent on theoxide basis, of 1.5-20% SiO₂, 225-25% Fe₂ O₃, 35-75% Al₂ O₃, 10-40%TiO₂, and 0.1-5% RE₂ O₃.
 2. A sintered ceramic article according toclaim 1 wherein said crystal phases, expressed in terms of volumepercent, consist essentially of about 25-90% iron-aluminum titanatesolid solution and about 5-70% mullite with the rare earth metal oxidecomprising up to the remainder.
 3. A sintered ceramic body as in claim 2wherein said solid solution consists essentially of, by weight percent,30 to 75 percent alumina, 20 to 65 percent titania, and >5 to 25 percentiron oxide.
 4. A sintered ceramic body as in claim 3 wherein said solidsolution is stable to within less than 20 percent of a totalstoichiometric decomposition, wherein said decomposition products areAl₂ O₃, Fe₂ O₃, and TiO₂, within the temperature range betweenapproximately 1000° C. to 1300° C.
 5. A sintered ceramic body as inclaim 1 wherein said rare earth oxide is selected from the groupconsisting essentially of lanthanum, cerium, praseodymium, neodymium,samarium, europium, gadolinium, terbium, dysprosium, erbium, ytterbium,yttrium, scandium, and/or a combination thereof.
 6. A sintered ceramicbody as in claim 1 wherein said body exhibits a coefficient of thermalexpansion between -25×10⁻⁷ /°C. and 25×10⁻⁷ /°C. (25°-800° C.).
 7. Asintered ceramic body as in claim 1 wherein said body exhibits a fourpoint bend MOR in the range from 1000 psi to 9000 psi.
 8. A sinteredceramic body as in claim 1 wherein said body exhibits a coefficient ofthermal cycling growth of less than 200×10⁻⁴ percent per cycle.
 9. Asintered ceramic body as in claim 1 wherein said body is a honeycomb.10. A sintered ceramic body consisting essentially of, by weightpercent, 50 to 75 percent iron-aluminum titanate solid solution, 20 to50 percent mullite, and 0.1 to 5 percent rate earth oxide.
 11. Asintered ceramic body as in claim 10 wherein the solid solution consistsessentially of, by weight percent, 35 to 50 percent alumina, 40 to 42percent titania, and 8 to 25 percent iron oxide.
 12. A sintered ceramicbody as in claim 10 wherein the solid solution consists essentialy of,by weight percent, 35 to 50 percent alumina, 40 to 42 percent titania,and 15 to 25 percent iron oxide.